1. Field of the Invention
The present invention relates to a method for controlling secondary battery charging and a control apparatus therefor. More particularly, the invention relates to a control method and a control apparatus for secondary battery charging, in a constant current charging control method, which detect completion of the battery charging and then stop the battery charging.
2. Description of the Related Art
Constant current charging methods are known for charging a secondary battery in a short time, for example, for charging a secondary battery to nominal capacity in one hour. In this charging method, it is necessary to detect completion of the battery charging process. Various methods are known for detecting the completion of battery charging, for example, as follows:
(a) A method by detecting a decrease in battery voltage from a maximum battery voltage (-.DELTA.V).
(b) A method by detecting an increase in battery temperature per unit time (.DELTA.T/.DELTA.t).
(c) A method by detecting an increase in battery voltage value per unit time (.DELTA.V/.DELTA.t).
In the method (a), if a reference value for comparing the value of -.DELTA.V is set too large, the battery will be overcharged and the battery temperature will increase excessively, thereby shortening the battery life.
In the method (b), if the ambient temperature increases during the battery charging period, the battery temperature will also increase. Therefore, the increased ambient temperature may be inadvertently detected as indicating that the battery is completely charged.
In the method (c), an increase in the battery voltage does not occur only before the battery is completely charged, but also occurs at the start of the battery charging. Therefore, the increased battery voltage at the start of the battery charging may be detected as indicating that the battery is completely charged.